Systems and methods for estimating exposure temperatures and remaining operational life of high temperature components

ABSTRACT

Non-destructive systems and methods for temperature measurements are described so that the remaining operational life and accumulated damage of high temperature gas turbine components can be assessed. Alloy-based witness coupons and diffusion couple witness coupons are attached to, or directly applied onto, high temperature components so that they experience the same high temperature operation and shut down as the components themselves. The witness coupons are later removed from the components and analyzed, or are analyzed on the component, to determine the change to their microstructure, metallurgy, and/or diffusion characteristics. Since the time each component spends in operation is known, the operating temperatures of the components can be back-calculated from the microstructural, metallurgical, and/or diffusion characteristic changes of the witness coupons. Therefrom, the remaining operational life of the component can be assessed, as can the accumulated damage to the component.

FIELD OF THE INVENTION

[0001] The present invention relates generally to systems and methodsfor estimating the temperatures experienced by a component,specifically, gas turbine hot-gas-path components. More specifically,the present invention relates to systems and methods that utilizeanalysis of the metallurgical changes of a material to estimate thetemperatures that a high temperature gas turbine component hasexperienced, so that, if desired, the remaining operational life andaccumulated damage of the component may be assessed therefrom.

BACKGROUND OF THE INVENTION

[0002] Measuring the temperatures that a high temperature turbinecomponent (i.e., hot-gas-path components such as blades, vanes and/orshrouds in a gas turbine) has experienced is very important so thatturbine design can be verified, metallurgical changes can be estimated,the remaining operational life of the component can be estimated,inspection intervals can be optimized, and operational conditions can beregulated. Such information is of great importance to both aircraft andpower generation industries. Components that work in high temperatureenvironments are particularly susceptible to degradation, the extent ofwhich depends on a number of factors, such as the creep rate, rupturestress, stress/strain amplitude of cyclic loading, corrosion and/orerosion rate, and thermal mechanical fatigue, among other things. Insome cases, such as when exposed to high temperatures for prolongedperiods of time, material undergoes metallurgical changes (i.e.,chemistry, microstructure, etc.) that reduce the material's reliabilityand durability. The degree of effect that these factors may have dependson the operational working temperatures of the components. Therefore,the temperatures that are experienced by a component are an importantparameter governing the life of such components, as is the time that isspent at these temperatures. As such, many life assessment procedureshave been developed to estimate the remaining operational life of suchcomponents based on the operating temperatures that these componentshave experienced, and the time they have spent in operation.

[0003] Currently, there are both destructive and non-destructive systemsand methods for estimating the temperatures that a gas turbine componenthas experienced during operation. Some destructive systems and methodsinvolve cutting up the component itself so that the characteristicmetallurgical changes in the component can be investigated, and thetime-temperature relationship can be estimated therefrom. Such methodsutilize calculations similar to the Larson-Miller relationship. Forexample, a relationship of a precipitation amount, a temperature, and atime of a characteristic phase may be obtained for a high temperaturegas turbine part formed of nickel-based single crystal alloy, and thetemperature and remaining operational life of this part may then beestimated from this relationship by investigating the microstructure ofthe part. Non-destructive systems and methods that have been used toestimate the temperatures that hot-gas-path components in gas turbineshave experienced include using thermocouples, pyrometers, eddy currentsensors and/or temperature probes, among other things.

[0004] These current systems and methods have significant drawbacks: 1)many require a laborious procedure; 2) many use a complex arrangement ofsensors; 3) many are barely able to sustain long hours at the hightemperatures that gas turbine components experience; 4) many are notresistant to the hostile environment (i.e., oxidation, corrosion) thatgas turbine components experience; 5) many are destructive to thecomponents themselves, and/or 6) many are not suitable for moving parts.Thus, there is a need for systems and methods that allow thetemperatures that such gas turbine components experience to be measuredor estimated more reliably, accurately, conveniently and easily. Thereis also a need for such systems and methods to allow the remainingoperational life and/or accumulated damage of such gas turbinecomponents to be assessed. There is yet a further need for such systemsand methods to be non-destructive to the gas turbine componentsthemselves. There is still a further need for such systems and methodsto utilize witness coupons for estimating the temperatures that such gasturbine components experience. There is also a need for such systems andmethods to utilize: 1) alloy-based witness coupons comprising at leastone alloy comprising at least two phases and having the characteristicfeature that the solubility of at least one element in one of the phaseschanges greatly with temperature changes, or 2) diffusion couple witnesscoupons comprising pure element couples such as rhodium-platinum, oralloy couples such as Co30Cr—Co20Cr10Al (weight %), or couplescomprising combinations of pure elements and alloys such as Pt—Co30Cr(weight %). There is also a need for such systems and methods toestimate the temperatures that are experienced by such gas turbinecomponents based on the metallurgical changes of the witness coupons.There is also a need for such systems and methods to estimate thetemperatures that are experienced by such gas turbine components basedon the diffusion characteristic changes of the witness coupons. Finally,there is a need for such systems and methods to be designed so they donot interfere with the aerodynamics and mechanical design of the gasturbine.

SUMMARY OF THE INVENTION

[0005] Accordingly, the above-identified shortcomings of existingsystems and methods are overcome by embodiments of the presentinvention. This invention relates to systems and methods for estimatingthe temperatures that a high temperature component (i.e., a gas turbinecomponent) has experienced, so that the remaining operational life andaccumulated damage of the component can be assessed. Embodiments of thisinvention comprise systems and methods that require no laboriousprocedure or complex arrangement of sensors, that are able to sustainlong hours at the high temperatures that gas turbine componentsexperience, that are resistant to the hostile environment that gasturbine components experience (i.e., that are oxidation and/or corrosionresistant), that are not destructive to the turbine componentsthemselves, and/or that are suitable for moving parts. In someembodiments, the systems and methods of this invention may allow thetemperatures that gas turbine components experience to be measured orestimated more reliably, accurately, conveniently and easily thancurrently possible. Embodiments of this invention may allow theremaining operational life and/or accumulated damage of such gas turbinecomponents to be assessed. In embodiments, this invention may benon-destructive to the gas turbine components themselves. Furthermore,embodiments of this invention can be designed so they utilize witnesscoupons for estimating the temperatures that such gas turbine componentsexperience. These witness coupons may comprise: I) alloy-based witnesscoupons comprising at least one alloy comprising at least two phases andhaving the characteristic feature that the solubility of at least oneelement in one of the phases changes greatly with temperature changes,or 2) diffusion couple witness coupons comprising pure element couplessuch as rhodium-platinum, or alloy couples such as Co30Cr—Co20Cr10Al(weight %), or couples comprising combinations of pure elements andalloys such as Pt—Co30Cr (weight %). The temperatures that gas turbinecomponents experience may be estimated based on the metallurgicalchanges of these witness coupons. Alternatively, the temperatures thatgas turbine components experience may be estimated based on thediffusion characteristic changes of these witness coupons. Finally,embodiments of this invention may be designed so they do not interferewith the aerodynamics and mechanical design of the gas turbine.

[0006] This invention comprises witness coupons that are useful forestimating the temperatures that high temperature gas turbine componentshave experienced. Since the time a component has spent in operation is aknown parameter (or one that can be easily found out), these estimatedtemperatures may then be used to determine how much operational liferemains for a given component, or to determine how much accumulateddamage has occurred to the component. As used herein, the term “witnesscoupon” comprises two different types of witness coupons: alloy-basedwitness coupons and diffusion couple witness coupons. The alloy-basedwitness coupons comprise an alloy containing at least two phases,wherein the alloy has the characteristic feature that the solubility ofat least one element in one of the phases changes greatly withtemperature changes. Additionally, other characteristic features of thealloy, such as the chemistry, lattice parameter, phase fraction, andelectrical or magnetic properties, may also change greatly according tovarious temperatures. The second type of witness coupons, the diffusioncouple witness coupons, comprise pure element couples such asrhodium-platinum, or alloy couples such as Co30Cr—Co20Cr10Al (wt. %), orcouples comprising a combination of pure elements and alloys such asPt—Co30Cr (wt. %). The diffusion couple witness coupons have thecharacteristic feature that there is interdiffusion between thecomponents of the diffusion couple (i.e., between the pure elementsand/or the alloys). The interdiffusion process is a function of time andtemperature, thus the changes of the characteristic properties of thediffusion couple witness coupons (i.e., interdiffusion distance,interdiffusion profile, chemistry at certain locations in theinterdiffusion zone, and the corresponding electrical and magneticproperties) are also functions of time and temperature.

[0007] Typically, high temperature gas turbine components experiencehigh operating temperatures for a given period of time, and are thenshut down. The shut down process is similar to a quenching process,where the component is quickly cooled down from the high operatingtemperature. The witness coupons of this invention may be attached to ahigh temperature gas turbine component so as not to interfere with theaerodynamics or mechanical design of the component. In this manner, thewitness coupon can experience the same high temperature operation andshut down as the component itself. These alloy-based witness coupons aredesigned so that the time spent at the high operating temperatureschanges the microstructure of the alloy in the alloy-based witnesscoupon, and the fast cooling of the component and the alloy-basedwitness coupon during the shut down process preserves the hightemperature microstructure in the alloy-based witness coupon. Thesediffusion couple witness coupons are designed so that the time spent atthe high operating temperatures causes interdiffusion between the pureelements and/or the alloys, which is preserved after the component isshut down. Since the witness coupons experience the same operational andshut down temperatures as the component itself, the witness couponscarry information about the operating temperature of the component.These witness coupons can then be removed from the component andanalyzed, or they can be analyzed while still on or attached to thecomponent, to determine the operating temperatures the component wasexposed to, and the remaining operational life of the component can bedetermined therefrom. The accumulated damage to the component may alsobe determined from the estimated operating temperatures of thecomponent.

[0008] One embodiment of this invention comprises the witness couponsthemselves. Other embodiments of this invention comprise systems andmethods for characterizing metallurgical changes and/or diffusioncharacteristic changes and estimating the temperatures that a hightemperature component has experienced so that the remaining operationallife and/or accumulated damage of the high temperature component can beassessed. Yet other embodiments of this invention comprise methods ofmaking and implementing the witness coupons.

[0009] This invention has all the advantages of existing systems andmethods, but it is non-destructive to the gas turbine componentsthemselves, and allows the remaining operational life and/or accumulateddamage of gas turbine components to be more easily, accurately,conveniently and reliably assessed.

[0010] Further features, aspects and advantages of the present inventionwill be more readily apparent to those skilled in the art during thecourse of the following description, wherein references are made to theaccompanying figures which illustrate some preferred forms of thepresent invention, and wherein like characters of reference designatelike parts throughout the drawings.

DESCRIPTION OF THE DRAWINGS

[0011] The systems and methods of the present invention are describedherein below with reference to various figures, in which:

[0012]FIG. 1 is a photograph showing several witness coupons of thepresent invention attached to the tip caps of turbine blades; and

[0013]FIG. 2 is a scanning electron microscopy (SEM) micrograph showingthe interdiffusion of Rh and Pt in one embodiment of a diffusion couplewitness coupon of this invention.

DETAILED DESCRIPTION OF THE INVENTION

[0014] For the purposes of promoting an understanding of the invention,reference will now be made to some preferred embodiments of the presentinvention as illustrated in FIGS. 1-2, and specific language used todescribe the same. The terminology used herein is for the purpose ofdescription, not limitation. Specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as abasis for the claims as a representative basis for teaching one skilledin the art to variously employ the present invention. Any modificationsor variations in the depicted systems and methods, and such furtherapplications of the principles of the invention as illustrated herein,as would normally occur to one skilled in the art, are considered to bewithin the spirit of this invention.

[0015] The present invention comprises witness coupons that are usefulfor estimating the temperatures that high temperature gas turbinecomponents have experienced. Since the times these components have spentin operation is a known parameter, the temperatures these componentshave experienced can be estimated, and may then be used to determine howmuch operational life remains for a given component. These estimatedtemperatures may also be used to determine how much damage has beenaccumulated to a given component. The alloy-based witness couponscomprise an alloy containing at least two phases, wherein the alloy hasthe characteristic feature that the solubility of at least one elementin one of the phases changes greatly with temperature changes.Additionally, other characteristic features, such as the chemistry,lattice parameter, phase fraction, hardness/modulus, and electrical ormagnetic properties, also change greatly in the alloy according tovarious temperatures.

[0016] The alloy-based witness coupons may be made in several differentmanners. A melting-solidification process may be used to make thesealloy-based witness coupons, where the alloy is first melted and thensolidified. These alloy-based witness coupons may also be made by adeposition process, such as by sputtering, thermal spraying, ion plasmadeposition, or the like. Another way these alloy-based witness couponsmay be made is by a powder deposition and sintering process, where thealloy and/or pure element mixture is deposited onto the area of intereston the component by direct-writing of inks containing metal powders,paste, or tape, then the mixture is consolidated by high temperaturesintering. These powder mixtures may also be processed by laser orelectron cladding processes.

[0017] One exemplary method of making an alloy-based witness couponcomprises: casting an alloy ingot of an alloy-based witness coupon usinginduction melting, arc melting, or the like; performing high temperatureannealing to homogenize the alloy ingot; and sectioning the alloy ingotinto appropriate sized alloy-based witness coupons that can be attachedto a high temperature component.

[0018] Another exemplary method of making an alloy-based witness couponcomprises: depositing a layer of a material onto a high temperaturecomponent using a direct-writing method, physical vapor deposition,chemical vapor deposition, or the like; and depositing additional layersof the material onto the high temperature component as desired to makean alloy-based witness coupon.

[0019] The diffusion couple witness coupons may be made by electron beamwelding the edges of metal foils, followed by hot isostatic pressing(HIP) at a predetermined temperature for a predetermined amount of time.These diffusion couple witness coupons may also be made by a depositionprocess, such as by sputtering, thermal spraying, ion plasma deposition,or the like. Another way these diffusion couple witness coupons may bemade is by a powder deposition and sintering process, where the alloyand/or pure element mixture is deposited onto the area of interest onthe component by direct-writing of inks containing metal powders, paste,or tape, then the mixture is consolidated by high temperature sintering.These powder mixtures may also be processed by laser or electroncladding processes.

[0020] One exemplary method of making a diffusion couple witness couponcomprises: pressing thin foils of metals together using cold pressing,cold isostatic pressing, hot isostatic pressing, or the like to makediffusion couple sheets; and then sectioning the diffusion couple sheetsinto appropriate sized diffusion couple witness coupons that can beattached to a high temperature component.

[0021] These manners of making the alloy-based witness coupons and thediffusion couple witness coupons are meant to be exemplary, notlimiting, examples of how these witness coupons can be made. Many othermethods of making these witness coupons are also possible, as will berecognized by those skilled in the art.

[0022] Before use, relationships of temperature-specific characteristicsof a witness coupon may first need to be established and catalogued. Forexample, the chemistry, lattice parameter/phase fraction,hardness/modulus, electric properties and/or magnetic properties, and/orthe diffusion distances at various temperatures, for a witness couponcould be established and calibrated corresponding to the applicableoperational temperature range of gas turbines. Any suitable methods maybe utilized to measure or determine the temperature-specificcharacteristics of the witness coupons.

[0023] For example, the chemistry of the alloy-based witness coupons maybe measured or determined by electron microprobe analysis using eitherwavelength dispersive spectroscopy (WDS) or energy dispersivespectroscopy (EDS), x-ray fluorescence, laser plasma spectroscopy, orthe like. The lattice parameter/phase fraction of the alloy-basedwitness coupons may be measured or determined by high energy x-ray,neutron diffraction analysis, image analysis integrating optical and/orelectron microscopy, or the like. The hardness/modulus of either thealloy-based witness coupons or the diffusion couple witness coupons maybe measured or determined by nanoindentation, microhardness testing,ultrasonic modulus measurement techniques, or the like. The electricproperties (in terms of resistivity and/or conductivity) of either thealloy-based witness coupons or the diffusion couple witness coupons maybe measured or determined by eddy current probe. The magnetic properties(in terms of magnetic field) of either the alloy-based witness couponsor the diffusion couple witness coupons can be measured or determined byeddy current probe. The diffusion characteristics (i.e., diffusiondistances at various temperatures) of the diffusion couple witnesscoupons can be measured or determined by electron microprobe analysisusing either wavelength dispersive spectroscopy (WDS) or energydispersive spectroscopy (EDS), or nanoindentation. Finally, the surfacemicro-voltage of either the alloy-based witness coupons or the diffusioncouple witness coupons may be measured by thermoelectric unitmeasurements.

[0024] Once the operational conditions are identified, and therelationships of the temperature-specific characteristics of a witnesscoupon are established, a witness coupon may then be attached to, orapplied directly onto, a high temperature gas turbine component so asnot to interfere with the aerodynamics or mechanical design of thecomponent. For example, as shown in FIG. 1, witness coupons 10 may beattached to the tip caps of a gas turbine blade 20 so that bladetemperatures can be measured and/or estimated. While the witness coupons10 depicted here are circular, any other suitable shape is alsofeasible. Witness coupons 10 could also be attached to any othersuitable component or location where the temperature condition duringoperation needs to be diagnosed or evaluated. Witness coupons 10 couldalso be applied as a coating, directly onto the surface of thecomponent. In either manner, the witness coupons can experience the samehigh temperature operation and shut down cycles as the component itself.

[0025] Witness coupons may be attached to any suitable desired locationon a turbine component in any suitable manner, such as by diffusionbonding, electron beam welding, laser welding, brazing, spraying,sputtering, ion plasma processing, suitable mechanical attachment means,or the like. Alternatively, the witness coupons may be directly writtenor deposited onto the component via a direct-write process, where thealloy is directly deposited onto the component via a melt-solidificationprocess, physical vapor deposition, chemical vapor deposition, or thelike. In addition, the alloy and/or pure element powder mixtures may bewritten onto the component and then be subsequently heat-treated atsuitable temperatures. The deposited powder may also be treated byelectron beam welding, or by a laser cladding process, or the like.

[0026] During operation, high temperature gas turbine componentstypically experience high operating temperatures for a given period oftime, and are then shut down. The shut down process is similar to aquenching process, where the component is quickly cooled down from thehigh operating temperature. These alloy-based witness coupons aredesigned so that the time spent at the high operating temperaturechanges the metallurgical characteristics of the alloy in thealloy-based witness coupon, and the fast cooling of the component andthe alloy-based witness coupon during the shut down process preservesthe high temperature microstructure in the alloy-based witness coupon.The metallurgical characteristic change in the alloy-based witnesscoupon can allow the last temperature and/or the average temperature ofa high temperature gas turbine component to be accurately estimatedtherefrom. The diffusion couple witness coupons are designed so that thetime spent at the high operating temperature causes the pure elementsand/or alloys to diffuse into one another in varying degrees. Thesediffusion characteristic changes can allow the average temperature of ahigh temperature gas turbine component to be accurately estimatedtherefrom.

[0027] Which temperature is estimated depends on the diffusion processof the elements in the alloy, and the time the component spends inoperation. For example, if the diffusion process is fast, such as in theCo—Al two-phase alloy-based witness coupon system, and the componentspends a long time in operation, the temperature estimated is the lasttemperature experienced by the component. If the diffusion process isslow, such as in the Co—Pt two-phase alloy-based witness coupon system,and the component spends a relatively short amount of time in operation(i.e., less than about 200 hours), the temperature estimated is theaverage temperature experienced by the component. In the case of thediffusion couple witness coupons, the estimated temperature is alwaysthe average temperature that is experienced by the component.

[0028] In the alloy-based witness coupons, the exposure or operatingtemperatures of the turbine components can be estimated by analyzing thephase formation of these witness coupons. During high temperatureoperation, the alloy in the alloy-based witness coupons is designed toexperience metallurgical changes (i.e., phase fraction, latticeparameter, etc.) according to various temperatures. The change of themetallurgical characteristics allows the exposure or operatingtemperatures of the alloy-based witness coupons to be evaluated. Sincethe time that a component is in operation is known, the operatingtemperatures can be back-calculated from the time and microstructural ormetallurgical changes that are observed in the alloy-based witnesscoupons.

[0029] In the diffusion couple witness coupons, the exposure oroperating temperatures of the turbine components can be estimated byanalyzing the diffusion kinetics of these diffusion couple witnesscoupons. During high temperature operation, the pure elements and/oralloys in the diffusion couple witness coupons are designed to interactand diffuse into one another to form intermetallic compounds orinterdiffusion zones according to various temperatures. The formation ofthese intermetallic compounds or interdiffusion zones, as well as thethickness of the zones, allows the exposure or operating temperatures ofthe diffusion couple witness coupons to be evaluated. An SEM micrographshowing the interdiffusion 50 between the rhodium (Rh) 30 and theplatinum (Pt) 40 in one diffusion couple witness coupon is shown in FIG.2. Since the time that a component is in operation is known, theoperating temperatures can be back-calculated from the diffusioncharacteristic changes that are observed in the diffusion couple witnesscoupons.

[0030] During a shut down of the turbine, or at any other suitable time,the witness coupons may be removed from the component, and the phaseformation and/or diffusion kinetics of the witness coupon can beanalyzed. Alternatively, the witness coupons may be analyzed while stillon, or attached to, the component. The analysis may be done eitherdestructively (i.e., via microprobe analysis or nanoindentation, etc.)or non-destructively (i.e., via x-ray diffraction or neutron diffractionanalysis, etc.). Preferably, if the witness coupon is still attached tothe component when the analysis is performed, the analysis will benon-destructive to the component itself.

[0031] For example, the chemistry or composition of the alloy-basedwitness coupons could be determined by electron microprobe analysis. Thediffusion profiles that are measured from electron microprobe analysisallow the temperature to be calculated based on the diffusioncoefficients of the materials in the alloy-based witness coupons. Whilethis is a destructive process to the alloy-based witness coupons, it isnon-destructive to the turbine component itself.

[0032] The lattice parameter/phase fraction of the alloy-based witnesscoupons could be determined by x-ray diffraction analysis or by neutrondiffraction analysis. This process is a non-destructive process, bothfor the alloy-based witness coupons and the turbine component itself.

[0033] The hardness/modulus of either the alloy-based witness coupons orthe diffusion couple witness coupons could be determined bynanoindentation. While this is a destructive process to the witnesscoupons, it is non-destructive to the turbine component itself.

[0034] The micro-voltage of either the alloy-based witness coupons orthe diffusion couple witness coupons could be determined bythermoelectric unit measurements. This measurement is based on thethermoelectric principle known as the Seebeck effect. This process is anon-destructive process, both for the witness coupons and the turbinecomponent itself.

[0035] The diffusion characteristics of the diffusion couple witnesscoupons could be determined by electron microprobe analysis using eitherwavelength dispersive spectroscopy (WDS) or energy dispersivespectroscopy (EDS), or nanoindentation. While this is a destructiveprocess to the diffusion couple witness coupons, it is non-destructiveto the turbine component itself.

[0036] The results of such analyses are representative of thecrystalline structure and chemical composition of the metal or alloybeing tested. The results of the analyzed witness coupons may then becompared to the calibrated and catalogued witness coupons, and theoperating temperatures of the witness coupons may be estimated therefrombased on the changes of the temperature-sensitive characteristics. Sincethe witness coupons experience the same temperature cycles as theturbine component it is attached to, the operating temperatures of thecomponent can therefore be obtained from the estimated temperatures thatthe witness coupons experienced. Thereafter, since the time that thecomponent has spent in operation is known, the remaining operating lifeand/or accumulated damage of the component can be determined based onthe temperature estimations.

[0037] The alloy-based witness coupons may comprise any suitable alloysthat comprise at least two phases and have the characteristic that thesolubility of at least one element in one of the phases changes greatlywith temperature changes, such as, for example, Co—Cr (where the Crcontent is about 65-80 wt. %), Pt—Cr (where the Cr content is about57-80 wt. %), or Co—Al (where the Al content is about 8-18 wt.

[0038] The diffusion couple witness coupons preferably comprise preciousmetals and/or their alloys, as well as an oxidation-resistant alloycomprising aluminum, chromium, silicon, titanium, etc. Precious metalsare preferred because they have outstanding oxidation and hot-corrosionresistance, both of which are necessary to survive the harsh, hightemperature environment in which turbines operate. Coating materialscomprising NiAl, Ni(Pt)Al, and MCrAlY, where M stands for Ni, Co or Fe,also exhibit outstanding oxidation and hot-corrosion resistance, andthey are also suitable as components of the diffusion couple witnesscoupons. The thickness of the diffusion couples depends on thetemperature and time that a particular high temperature componentexperiences. The thickness should be sufficient so that completehomogenization of the compositions does not occur.

[0039] Embodiments of this invention comprise methods for estimating thetemperatures that a high temperature component has experienced so thatthe remaining operational life of the high temperature component can beassessed. In one embodiment, the method comprises: attaching a witnesscoupon to the high temperature component; allowing the component and thewitness coupon to cycle through at least one cycle of high temperatureoperation and shut down; analyzing the witness coupon; and estimatingthe temperatures that the high temperature component has experiencedbased on the data acquired by analyzing the witness coupon. This methodmay further comprise the steps of: removing the witness coupon from thehigh temperature component prior to analyzing the witness coupon,estimating the remaining operational life of the high temperaturecomponent, and/or estimating the accumulated damage to the hightemperature component.

[0040] The attaching step may comprise the following steps, or means forperforming the following steps: mechanically attaching the witnesscoupon onto the high temperature component, diffusion bonding thewitness coupon onto the high temperature component, electron beamwelding the witness coupon onto the high temperature component, laserwelding the witness coupon onto the high temperature component, brazingthe witness coupon onto the high temperature component, spraying thewitness coupon onto the high temperature component, sputtering thewitness coupon onto the high temperature component, ion plasmaprocessing the witness coupon onto the high temperature component,directly depositing the witness coupon onto the high temperaturecomponent via a melt-solidification process, directly depositing thewitness coupon onto the high temperature component via physical vapordeposition, directly depositing the witness coupon onto the hightemperature component via chemical vapor deposition, depositing thewitness coupon onto the high temperature component via a laser claddingprocess, depositing the witness coupon onto the high temperaturecomponent via an electron cladding process, depositing a powder onto thehigh temperature component followed by consolidation of the powder viasintering, depositing a paste onto the high temperature componentfollowed by consolidation of the paste via sintering, and/or depositinga tape onto the high temperature component followed by consolidation ofthe tape via sintering.

[0041] The analyzing step may comprise the following steps, or means forperforming the following steps: electron microprobe analysis usingeither wavelength dispersive spectroscopy or energy dispersivespectroscopy, x-ray fluorescence, laser plasma spectroscopy, high energyx-ray, neutron diffraction analysis, image analysis integrating opticalmicroscopy, image analysis integrating optical or electron microscopy,nanoindentation, microhardness testing, ultrasonic modulus measurementtechniques, eddy current probing, and/or thermoelectric unitmeasurements.

[0042] The witness coupons of this invention may comprise alloy-basedwitness coupons or diffusion couple witness coupons. The alloy-basedwitness coupons may comprise: an alloy comprising at least two phases, abinary alloy comprising cobalt and chromium, a binary alloy comprisingplatinum and chromium, a binary alloy comprising cobalt and aluminum,and/or a binary alloy comprising a precious metal. The diffusion couplewitness coupon may comprise: Co30CrCo20Cr10Al (weight %), Pt—Co30Cr(weight %), rhodium, platinum, palladium, a precious metal, and/or analloy of a precious metal. The diffusion couple witness coupon mayfurther comprise a coating comprised of: NiAl, Ni(Pt)Al, and/or MCrAlY,where M stands for Ni, Co or Fe as members of the couples or as aprotective coating of the diffusion couples.

[0043] Embodiments of this invention also comprise systems forestimating the temperatures that a high temperature component hasexperienced so that the remaining operational life of the hightemperature component can be assessed. In one embodiment, these systemscomprise: a means for attaching a witness coupon to the high temperaturecomponent; a means for allowing the component and the witness coupon tocycle through at least one cycle of high temperature operation and shutdown; a means for analyzing the witness coupon; and a means forestimating the temperatures that the high temperature component hasexperienced based on the data acquired by analyzing the witness coupon.These systems may further comprise: a means for removing the witnesscoupon from the high temperature component prior to analyzing thewitness coupon, a means for estimating the remaining operational life ofthe high temperature component, and/or a means for estimating theaccumulated damage to the high temperature component.

[0044] Embodiments of this invention also comprise methods of making awitness coupon. In one embodiment, the method may comprise: casting analloy ingot of an alloy-based witness coupon using induction melting,arc melting, or the like; performing high temperature annealing tohomogenize the alloy ingot; and sectioning the alloy ingot intoappropriate sized alloy-based witness coupons that can be attached to ahigh temperature component. In another embodiment, the method maycomprise: depositing a layer of a material onto a high temperaturecomponent using micro-pen direct-write method, physical vapordeposition, chemical vapor deposition, or the like; depositingadditional layers of the material onto the high temperature component asdesired to make an alloy-based witness coupon. In yet anotherembodiment, the method may comprise: pressing thin foils of metalstogether using cold pressing, cold isostatic pressing, hot isostaticpressing, or the like to make diffusion couple sheets; sectioning thediffusion couple sheets into appropriate sized diffusion couple witnesscoupons that can be attached to a high temperature component.

[0045] As described above, the systems and methods of the presentinvention allow the remaining operational life of gas turbine componentsto be easily, accurately, conveniently and reliably assessed.Advantageously, these systems and methods are also non-destructive tothe turbine components themselves.

[0046] Various embodiments of the invention have been described infulfillment of the various needs that the invention meets. It should berecognized that these embodiments are merely illustrative of theprinciples of various embodiments of the present invention. Numerousmodifications and adaptations thereof will be apparent to those skilledin the art without departing from the spirit and scope of the presentinvention. For example, while this invention has been described in termsof witness coupons for use in gas turbines, numerous other applicationsof these witness coupons are possible—for example, these witness couponsmay be useful to other applications involving a hostile environmentand/or rotating parts. Thus, it is intended that the present inventioncover all suitable modifications and variations as come within the scopeof the appended claims and their equivalents.

What is claimed is:
 1. A method for estimating the temperatures that ahigh temperature component has experienced so that the remainingoperational life and the accumulated damage of the high temperaturecomponent can be assessed, the method comprising: attaching a witnesscoupon to the high temperature component; allowing the component and thewitness coupon to cycle through at least one cycle of high temperatureoperation and shut down; analyzing the witness coupon; and estimatingthe temperatures that the high temperature component has experiencedbased on the data acquired by analyzing the witness coupon.
 2. Themethod of claim 1, wherein the attaching step comprises at least one of:mechanically attaching the witness coupon onto the high temperaturecomponent, diffusion bonding the witness coupon onto the hightemperature component, electron beam welding the witness coupon onto thehigh temperature component, laser welding the witness coupon onto thehigh temperature component, brazing the witness coupon onto the hightemperature component, spraying the witness coupon onto the hightemperature component, sputtering the witness coupon onto the hightemperature component, ion plasma processing the witness coupon onto thehigh temperature component, directly depositing the witness coupon ontothe high temperature component via a melt-solidification process,directly depositing the witness coupon onto the high temperaturecomponent via physical vapor deposition, directly depositing the witnesscoupon onto the high temperature component via chemical vapordeposition, depositing the witness coupon onto the high temperaturecomponent via a laser cladding process, depositing the witness coupononto the high temperature component via an electron cladding process,depositing a powder onto the high temperature component followed byconsolidation of the powder via sintering, depositing a paste onto thehigh temperature component followed by consolidation of the paste viasintering, and depositing a tape onto the high temperature componentfollowed by consolidation of the tape via sintering.
 3. The method ofclaim 1, further comprising: removing the witness coupon from the hightemperature component prior to analyzing the witness coupon.
 4. Themethod of claim 1, wherein the analyzing step comprises at least one of:electron microprobe analysis using at least one of wavelength dispersivespectroscopy and energy dispersive spectroscopy; x-ray fluorescence;laser plasma spectroscopy; high energy x-ray; neutron diffractionanalysis; image analysis integrating optical microscopy; image analysisintegrating optical microscopy; image analysis integrating electronmicroscopy; nanoindentation; microhardness testing; ultrasonic modulusmeasurement techniques; eddy current probing; and thermoelectric unitmeasurements.
 5. The method of claim 3, wherein the analyzing stepcomprises at least one of: electron microprobe analysis using at leastone of wavelength dispersive spectroscopy and energy dispersivespectroscopy; x-ray fluorescence; laser plasma spectroscopy; high energyx-ray; neutron diffraction analysis; image analysis integrating opticalmicroscopy; image analysis integrating optical microscopy; imageanalysis integrating electron microscopy; nanoindentation; microhardnesstesting; ultrasonic modulus measurement techniques; eddy currentprobing; and thermoelectric unit measurements.
 6. The method of claim 1,further comprising: estimating the remaining operational life of thehigh temperature component.
 7. The method of claim 1, furthercomprising: estimating the accumulated damage to the high temperaturecomponent.
 8. The method of claim 1, wherein the witness couponcomprises an alloy-based witness coupon.
 9. The method of claim 8,wherein the alloy-based witness coupon comprises at least one of: analloy comprising at least two phases, a binary alloy comprising cobaltand chromium, a binary alloy comprising platinum and chromium, a binaryalloy comprising cobalt and aluminum, and a binary alloy comprising aprecious metal.
 10. The method of claim 1, wherein the witness couponcomprises a diffusion couple witness coupon.
 11. The method of claim 10,wherein the diffusion couple witness coupon comprises at least one of:Co30Cr—Co20Cr10Al (weight %), Pt—Co30Cr (weight %), rhodium, platinum,palladium, a precious metal, and an alloy of a precious metal.
 12. Themethod of claim 10, wherein the diffusion couple witness coupon furthercomprises a protective coating.
 13. The method of claim 12, wherein thecoating comprises at least one of: NiAl, Ni(Pt)Al, and MCrAlY, where Mstands for Ni, Co or Fe.
 14. A system for estimating the temperaturesthat a high temperature component has experienced so that the remainingoperational life and the accumulated damage of the high temperaturecomponent can be assessed, the system comprising: a means for attachinga witness coupon to the high temperature component; a means for allowingthe component and the witness coupon to cycle through at least one cycleof high temperature operation and shut down; a means for analyzing thewitness coupon; and a means for estimating the temperatures that thehigh temperature component has experienced based on the data acquired byanalyzing the witness coupon.
 15. The system of claim 14, wherein themeans for attaching a witness coupon to the high temperature componentcomprises at least one of: a means for mechanically attaching thewitness coupon onto the high temperature component, a means fordiffusion bonding the witness coupon onto the high temperaturecomponent, a means for electron beam welding the witness coupon onto thehigh temperature component, a means for laser welding the witness coupononto the high temperature component, a means for brazing the witnesscoupon onto the high temperature component, a means for spraying thewitness coupon onto the high temperature component, a means forsputtering the witness coupon onto the high temperature component, ameans for ion plasma processing the witness coupon onto the hightemperature component, a means for directly depositing the witnesscoupon onto the high temperature component via a melt-solidificationprocess, a means for directly depositing the witness coupon onto thehigh temperature component via physical vapor deposition, a means fordirectly depositing the witness coupon onto the high temperaturecomponent via chemical vapor deposition, a means for depositing thewitness coupon onto the high temperature component via a laser claddingprocess, a means for depositing the witness coupon onto the hightemperature component via an electron cladding process, a means fordepositing a powder onto the high temperature component followed byconsolidation of the powder via sintering, a means for depositing apaste onto the high temperature component followed by consolidation ofthe paste via sintering, and a means for depositing a tape onto the hightemperature component followed by consolidation of the tape viasintering.
 16. The system of claim 14, further comprising: a means forremoving the witness coupon from the high temperature component prior toanalyzing the witness coupon.
 17. The system of claim 14, wherein themeans for analyzing the witness coupon comprises at least one of:wavelength dispersive spectroscopy and energy dispersive spectroscopy;x-ray fluorescence; laser plasma spectroscopy; high energy x-ray;neutron diffraction analysis; image analysis integrating opticalmicroscopy; image analysis integrating optical microscopy; imageanalysis integrating electron microscopy; nanoindentation; microhardnesstesting; ultrasonic modulus measurement techniques; eddy currentprobing; and thermoelectric unit measurements.
 18. The system of claim16, wherein the means for analyzing the witness coupon comprises atleast one of: wavelength dispersive spectroscopy and energy dispersivespectroscopy; x-ray fluorescence; laser plasma spectroscopy; high energyx-ray; neutron diffraction analysis; image analysis integrating opticalmicroscopy; image analysis integrating optical microscopy; imageanalysis integrating electron microscopy; nanoindentation; microhardnesstesting; ultrasonic modulus measurement techniques; eddy currentprobing; and thermoelectric unit measurements.
 19. The system of claim14, further comprising: a means for estimating the remaining operationallife of the high temperature component.
 20. The system of claim 14,further comprising: a means for estimating the accumulated damage to thehigh temperature component.
 21. The system of claim 14, wherein thewitness coupon comprises an alloy-based witness coupon.
 22. The systemof claim 21, wherein the alloy-based witness coupon comprises at leastone of: an alloy comprising at least two phases, a binary alloycomprising cobalt and chromium, a binary alloy comprising platinum andchromium, a binary alloy comprising cobalt and aluminum, and a binaryalloy comprising a precious metal.
 23. The system of claim 14, whereinthe witness coupon comprises a diffusion couple witness coupon.
 24. Thesystem of claim 23, wherein the diffusion couple witness couponcomprises at least one of: Co30Cr—Co20Cr10Al (weight %), Pt—Co30Cr(weight %), rhodium, platinum, palladium, a precious metal, and an alloyof a precious metal.
 25. The system of claim 23, wherein the diffusioncouple witness coupon further comprises a protective coating.
 26. Thesystem of claim 25, wherein the coating comprises at least one of: NiAl,Ni(Pt)Al, and MCrAlY, where M stands for Ni, Co or Fe.
 27. A method ofmaking an alloy-based witness coupon, the method comprising the stepsof: casting an alloy ingot; annealing the cast alloy ingot to homogenizethe cast alloy ingot; and sectioning the annealed cast alloy ingot intopredetermined sized sections to form the alloy-based witness coupons.28. The method of claim 27, wherein the casting step comprises at leastone of: induction melting and arc melting.
 29. The method of claim 27,wherein the alloy-based witness coupon comprises at least one of: analloy comprising at least two phases, a binary alloy comprising cobaltand chromium, a binary alloy comprising platinum and chromium, a binaryalloy comprising cobalt and aluminum, and a binary alloy comprising aprecious metal.
 30. A method of making an alloy-based witness coupon,the method comprising the steps of: depositing a layer of a materialonto a high temperature component; and repeating the depositing step asmany times as necessary to create the desired alloy-based witnesscoupon.
 31. The method of claim 30, wherein the depositing layercomprises at least one of: directly writing the material onto the hightemperature component, physical vapor deposition of the material ontothe high temperature component, chemical vapor deposition of thematerial onto the high temperature component, sputtering the materialonto the high temperature component, thermal spraying the material ontothe high temperature component, ion plasma deposition of the materialonto the high temperature component, applying a paste of the materialonto the high temperature component followed by consolidation of thematerial via sintering, applying a tape comprising the material onto thehigh temperature component followed by consolidation of the material viasintering, powder deposition of the material onto the high temperaturecomponent followed by consolidation of the material via sintering, lasercladding the material onto the high temperature component, and electroncladding the material onto the high temperature component.
 32. Themethod of claim 30, wherein the alloy-based witness coupon comprises atleast one of: an alloy comprising at least two phases, a binary alloycomprising cobalt and chromium, a binary alloy comprising platinum andchromium, a binary alloy comprising cobalt and aluminum, and a binaryalloy comprising a precious metal.
 33. A method of making a diffusioncouple witness coupon, the method comprising the steps of: placing twometal foils together; joining the two metal foils together; andsectioning the joined metal foils into predetermined sized sections toform one or more diffusion couple witness coupons.
 34. The method ofclaim 33, wherein the joining step comprises at least one of: weldingthe edges of the two metal foils together, hot isostatically pressingthe two metal foils together, and cold isostatically pressing the twometal foils together.
 35. The method of claim 33, wherein the diffusioncouple witness coupon comprises at least one of: Co30Cr—Co20Cr10Al(weight %), Pt—Co30Cr (weight %), rhodium, platinum, palladium, aprecious metal, and an alloy of a precious metal.
 36. The method ofclaim 33, wherein the diffusion couple witness coupon comprises aprotective coating.
 37. The method of claim 36, wherein the coatingcomprises at least one of: NiAl, Ni(Pt)Al, and MCrAlY, where M standsfor Ni, Co or Fe.
 38. A method for estimating the temperatures that ahigh temperature component has experienced so that the remainingoperational life and the accumulated damage of the high temperaturecomponent can be assessed, the method comprising: attaching analloy-based witness coupon to the high temperature component; allowingthe component and the alloy-based witness coupon to cycle through atleast one cycle of high temperature operation and shut down; analyzingthe alloy-based witness coupon; and estimating the temperatures that thehigh temperature component has experienced based on the data acquired byanalyzing the alloy-based witness coupon, wherein the alloy-basedwitness coupon comprises an alloy comprising at least two phases whereinthe solubility of at least one element in one of the phases changesgreatly with temperature changes.
 39. A method for estimating thetemperatures that a high temperature component has experienced so thatthe remaining operational life and the accumulated damage of the hightemperature component can be assessed, the method comprising: attachinga diffusion couple witness coupon to the high temperature component;allowing the component and the diffusion couple witness coupon to cyclethrough at least one cycle of high temperature operation and shut down;analyzing the diffusion couple witness coupon; and estimating thetemperatures that the high temperature component has experienced basedon the data acquired by analyzing the diffusion couple witness coupon.